The purpose of this project is to determine the effects of light on the structure and conformation of model nucleic acids, and how alterations in structure and conformation relate to modified biological activities (mutagenesis and carcinogenesis). Oligonucleotides of defined base sequence will be synthesized. The oligomers will be irradiated with 254 nm or 310 nm light. The oligomer-photoproducts will be separated and purified by TLC and HPLC, and characterized by UV, NMR, and mass spectroscopy. The conformation of normal ribosyl- and deoxyribosyl-oligomers will be compared to their photoproduct-counterparts by multi-nuclear magnetic resonance spectroscopy, x-ray crystallography whenever possible, and computer graphic model building techniques.